Semiconductor devices can be constructed vertically or laterally. Compared with lateral semiconductor devices, vertical semiconductor devices have an increased integration density with regard to the semiconductor device surface area. Transistor semiconductor devices with a vertical construction are usually designed as trench semiconductor devices. The construction of a vertical power transistor realized as a trench semiconductor device will be explained in more detail below with reference to FIG. 1.
FIG. 1 shows a detail from a transistor 1 formed in a semiconductor zone 2. A plurality of trenches 3 are provided in the semiconductor zone 2, a field plate 4, a gate electrode 5, a gate oxide layer 6 and also a field oxide layer 7 being provided in each case within the trenches 3. The semiconductor zone 2 has a plurality of source zones 8 body zones 9 and also drain or drift zones 10. The source and body zones 8, 9 are electrically connected to a metallization layer 12 via a poly plug 11. The gate electrodes 5 are electrically insulated from the metallization layer 12 by an insulation structure 13.
Although the transistor 1 shown in FIG. 1 is constructed vertically and thus has an increased integration density relative to a transistor with a lateral construction, a width B of the trenches 3 on the top side of the transistor 1 is considerable, which means that the percentage proportion of the semiconductor device surface area required by the trenches 3 is not negligible. The width B of the trenches 3 cannot be reduced arbitrarily, however, since a relatively thick oxide layer, the field oxide layer 7, and optionally an additional field electrode is required in the lower region of the trenches 3 for the reliable functioning of the transistor 1. The width B of the trenches 3 thus depends on the thickness of the field oxide layer 7: the thicker the field oxide layer 7, the greater the width B of the trenches 3 must be as well.
The object on which the invention is based is to provide a method by which the width of the trenches in semiconductor devices with a vertical construction can be reduced, and, at the same time, the thickness of the field oxide layer provided in the trenches can be retained.